Growing Heat Tolerant Cymbidiums in Tropical Climates

(by Kobsukh Kaenratana)
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Growing heat-tolerant cymbidiums (HTCs) in tropical climates is easy and low maintenance. The ease is comparable to growing dendrobium hybrids, which is usually the starting point for beginners. HTCs generally can stand the impact of rainfall; therefore they do not need a rainproof roof.

Most cymbidiums enjoy good ventilation and moderate humidity. It is not advisable to grow cymbidiums with other high-humidity genera or under hanging baskets of other orchids. Though cymbidiums do not enjoy high humidity, they need to remain moist at the root ball. It is important that the growing medium is well-drained, yet retains some moisture well.

Pots should not be placed on the ground or closer than 18” to it as this will allow fungal diseases to infect the root ball. However, placing cymbidium pots directly on a dry clean surface, such as a balcony or terrace is acceptable. One precaution is to watch for water trapped at the bottom of the pot. To solve this problem, pots with one or two holes on the side of pot near the base are suggested. Another solution is to use pots with standing legs that prevent the bottom holes from contacting the floor. When cymbidium pots are placed in a well-ventilated location without exposure to strong & direct sunlight, growing cymbidiums is quite easy.

Light and Growing Location
In most tropical climates, 60-70% shade cloth is suggested for most HTCs. This rather heavy shade cloth will help prevent leaf burn during the hottest and driest months when the sun shines directly from above; peak sunlight in upper Thailand comes during March through May. Shade might be reduced whenever clouds and rains are more prevalent throughout even in the summer months. Less shade is also appropriate in the southern peninsula of Thailand, where heat is reduced by the nearby seas.

Growing in a home garden requires a well-ventilated The area should not be exposed to direct sunlight in the afternoon. However the desirable intensity of sunlight for each cultivar can be quite different. It depends on the different species in the background of the hybrid. For example, hybrids with a heavy background of C. ensifolium can tolerate areas of particularly heavy shade and poorer ventilation. In contrast, hybrids with a large proportion of C. canaliculatum in the background prefer greater sunlight, very good ventilation and a drier environment.

Importantly, most cymbidium hybrids will not yield any bloom if plants are placed under other hanging orchids.

Pots and Medium
Clay pots are the best for growing cymbidiums in tropical climates as the porosity of the clay encourages evaporative cooling during hot weather. This is the real advantage over plastic pots. In addition, the heavier weight of clay pots helps increase stability for cymbidiums with large top growth. Taller pots also add another advantage as the depth allows better roots development. This increases the overall health and energy storage of the plant. In addition to the bottom hole, a few additional side holes near the bottom of the pot will prevent water from standing at the bottom, which might cause root rot.

In general, baskets are not the preferred pot for growing most cymbidium hybrids. There are some exceptions, such as species that are highly epiphytic, including C. dayanum, C. lowianum, C. aloifolium, C. atropurpureum, and C. madidum. Baskets are only suitable for those species that form upright pnuematophores (upright aerial roots). It should be kept in mind that the terrestrial root trait always dominates epiphytic root traits in hybridizing. This explains why most hybrids should be grown in pot rather than basket, as most hybrids are the combination of both terrestrial and epiphytic species.

The base of the pseudobulbs should be placed on the surface of medium as this keeps good ventilation around the bulbs, thus preventing any rot problems in monsoon season.

There always seems to have a common misunderstanding in perceiving and treating cymbidium as a terrestrial plant. Many people try to grow cymbidium with soil or soil-like medium. This almost always leads to root rot. The resultant demise will be fast, especially in hot and humid weather, but will be delayed in cool climates.

Growers should select the media that fit their local climates, something locally available and that do not break down too soon. Examples include hydroton balls, charcoal, volcanic rock, construction rock, broken pieces of new clay pot and quality pine bark. All mediums should be in the size of 1/2”-1”. Sphagnum moss is a very good choice for the mix.

In many cases, staking the newly repotted plants is essential for the success. If plants are grown in loose mediums that allow plants to shake, it will take a very long time for the plants to establish.

In areas with less rain, such as upper Thailand (central plain, north and northeast region), the proportion of pine barks can be increased or some sphagnum moss might be added at the bottom to stabilize the moisture during the dry season. When moisture is constant, roots will grow faster.

It is common that pH in a medium drops to an undesirably acidic level over 3-4 years. Low pH is harmful to cymbidium roots and this will retard growth and reduce flower productivity. Adding or mixing Dolomite with the medium when the plant is potted helps regulate the pH. The prolonged proper pH level can prevent the plant from being damaged by bacterial and fungal infections. In addition, calcium and magnesium in Dolomite will boost growth vigor and spike productivity.

For deflasked cymbidium plantlets, the agar should be removed. It is better to grow plantlets in a medium such as sand or rice-husk charcoal in trays or community pots. Unlike other epiphytic orchids such as dendrobiums, vandas, and oncidiums, cymbidium plantlets will not tolerate drought or being bare-root. They will dehydrate quickly and die.

Once plantlets are well established, they should be moved to individual 3”-4” pots with coarser media, such as small coconut chips of 0.5”-1” size. They will grow in these small pots about one year before needing to move to the final, blooming size, 5”-6” pots with regular media mix.

Diseases and Pests
Most diseases and pests of cymbidiums are common among other orchids. Basic fungicides like Orthocide (Captan) and common pesticides like Carbaryl (Savin) still work well. Herein, typical and common problems for cymbidiums are mentioned.

1) Red Spider Mites can be more common to cymbidiums than to other orchid genera because of the soft long arching leaves, which are suitable for mites to dwell underneath.
Symptoms: Plants stop growing, leaves turn patchy yellow or colorless and dry, necrosis appears in older leaves, white spider web and red mites are found under leaves.
Treatment: Spray with Propargite (Omite) alternately with other miticides such as Pyridaben every seven days and emphasize spraying the underside of the leaves.

2) Bacterial Rot can cause damage from time to time, especially in monsoon season with poor ventilation. Another possible factor is too low a pH in the potting medium.
Symptoms: Brownish, soft, wet rot occurs on new young shoots.
Treatment: Improve ventilation and raise pH by adding dolomite. Repotting with new medium is recommended. Move the infected plant away from water and rain for a week.


3) Fungal Rot is usually caused by soil-borne fungi, mainly Fusarium wilt.
Symptoms: Soft rot, but not as wet as bacterial rot; occurs on new young shoots.
Treatment : Raise pH in medium by adding Dolomite or change the whole mix. Prevent the mix from contact with contaminated soils. Improve ventilation and spray with Terachlor if necessary.

4) Virus can cause hidden problems to all orchid growers. In fact, there are many viruses that cause diseases in orchids, but the two most common ones are CyMV (Cymbidium Mosaic Virus) and ORSV (Odontoglossum Ringspot Virus). It is possible that infected plants may not show any sign of viral symptoms.
Symptoms: The most common symptom is chlorosis on leaves. This is caused by the lack of chlorophyll in damaged cells; thus that area appears colourless or yellowish instead of green. In some cases, chlorosis occurs on floral tissue where it creates small colourless patches on flowers.

Since there is no cure for a virus-infected plant, it is crucial to understand the mechanism of spreading virus so that growers effectively can prevent the spread of virus.

Prevention:
• Cutting tools must be blazed or burn or treated with antiseptic agents before use between each plant.
• Never use recycled water from other orchids.
• Keep control of viral vectors such as spider mites, thrips and aphids.
• Keep good ventilation and enough sunlight around the growing area.
• Never pollinate with pollen from virus-infected plants.
• Never reuse pots and potting mixes.

5) Thrips and Aphids can be widely spread during dry periods.
Symptoms: Receding colour or colourless patches and burns on floral tissue.
Treatment: Spray with pesticide such as Carbaryl (Savin) or Methomyl (Lannate) every 2-3 weeks.

Watering and Fertilizing
Most cymbidiums hybrids are not sensitive to less desirable water quality. They can tolerate water with higher dissolved minerals than many other orchids. This characteristic becomes more evident with the hybrids that have a large proportion of terrestrial species in the background.

Watering cymbidiums can be done every day or once every week, depending on rainfall, moisture, and the ability to hold water and moisture of the potting mix. Watering cymbidiums should not be done more than once a day even on a very dry day.

Besides spraying fertilizer weekly, slow-released type fertilizer should be applied on top of the medium. Magnesium (Mg) as an additional micronutrient can be added a few months prior the end of the monsoon season or the start of blooming season for boosting the bloom.

Taking Care of Flower Spikes
For cool-growing cymbidiums, key factors to initiate flower spike and spike elongation are low-enough night temperature accompanying with minimal 10-degree differential day-night temperature. However, these two factors become less relevant and less pronounced for HTCs.

During the period of breaking flower sheath, plant should not be moved around to many different locations. To help reduce chance of bud drop in tropical weather, plant with spike should be moved to a shadier location or grower must provide more shade clothe.

Propagation (Division)
A sign to repot is when the plant has formed a big clump and its root ball has pushed the whole plant upward or even breaking its pot. Another less desirable sign to repot is when the plant lost vigour and blooming productivity. This is because the medium has stayed in the pot for so many years, thus pH has dropped down to too acidic level. This condition makes roots damaged and rotted.

Dividing cymbidium can follow the same rule as we do with other orchid genera such as Cattleya. Each new division should be composed of at least 2-3 mature bulbs plus one leading new shoot/bulb. Apply the cutting wound with fungicide after cutting. Healthy root ball is usually dense and well pact. Big knife or, sometimes, saw is needed to divide them.

Backbulb can be planted in tray of sand or rice-husk charcoal. In a few months, new shoot will emerge from the base of backbulb. Then, move to 4” pot.

Dividing should be done during the start of growing cycle, which generally matches the start of monsoon season. This timing helps the plant to recover faster and will be able to bloom in the next blooming season. One should not divide and repot at the end of growing cycle period or the end of rainy season as this means a waste of another blooming year since newly repotted divisions will not grow right away after repotting.

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Create Date : 22 พฤศจิกายน 2551		6 comments
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